Which render engine renders faster? Blender Internal or Cycles?
Blender internal is much faster is the jist of the situation. However the topic of which is the fastest is much more complex than that. 

Blender internal renders completely differently, using a 'biased' method. This means it is biased as to which light rays it follows (the important ones). This is generally faster and cleaner than cycles renderings but less realistic. It uses short cuts to simulate the flow of light. Its lighting model is more simplistic and easier to compute.

Cycles is 'unbiased'. It shoots light rays everywhere and you have to wait for the image to become acceptable in terms of random noise. If noise is okay in your image, it may be possible that cycles can render faster than blender internal. Most people dislike noise in their images, and to clean up all the noise it can take a very long time, especially for certain light rays like reflections and refractions.

Comparing the two in terms of performance is not really a useful exercise because they will give different results. It will be comparing apples to oranges best case. You use cycles if you want very close to realism. Blender internal can be used for less realistic rendering. Blender internal can be made more realistic if you have a great deal of skill.